You would want to use ambient occlusion because it shows subtle variations in lighting and helps your eyes detect surface details that would otherwise be washed out or unnoticeable. Ambient occlusion is great for softening the overall lighting in your scene if it's too bright.

How does ambient occlusion affect performance?

Whilst Ambient Occlusion was once a very demanding process, fine-tuning as well as more powerful GPUs mean AO has a very small impact on performance. You will experience lowered frame rates in certain circumstances but the base AO settings will offer a decent enough visual experience.

Should I enable ambient occlusion?

Screen space ambient occlusion is a great method in which to develop certain games, and especially great when running a game on perhaps an older PC, or one with low CPU power. ... Something that might appeal to game designers is that SSAO has no load times, making their game run smoother.